State Circle EarthCache
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Here you can find a road cutting which was exposed when the state circle was constructed. As this EarthCache is located next to a road, please do not stop with your car here but use the nearby car park of the National Library or Old Parliament House.
State Circle Earthcache S35 18.290 E149 07.622 The State Circle road cutting, approximately 320 metres long, exposes the unconformity between the slumped and faulted Early Silurian rocks (State Circle Shale) and overlying gently folded Middle to Late Silurian Units (Camp Hill Sandstone) is exposed. The rocks here are nicely weathered so that all features can be easily observed.
Near new Parliament House a plaque provides the profile and a short description of this outcrop. (It is located at S 35 18.298 E 149 07.634 ).
Please be careful when approaching this site, as the site is located right next to the adjacent traffic lanes. If you stay on the pedestrian path you are safe. You cannot park on the roadside but parking is available nearby and within easy walking distance of the outcrop. Parking is available near parliament house and at this location S 35 18.315 E 149 07.762
This unconformity is a significant geological feature and provides keys to the interpretation of the ancient landscape of the Canberra region. It is listed by the Geological Society of Australia as of national and international significance.
But what created these sediments?
Approximately 430 million years ago a large and deep sea covered this area and fine grained silty sediments were deposited. Later these rocks became compacted to the rocks of the state circle. But nearby the seafloor was sloped and on this slope other sediments blocks slided down slope and created slump folds. These folds are not tectonically created. Not much later (about 425 million years before present) the rocks became uplifted to above the sea level. During the lifting process the rocks became folded and faulted. After the uplift the rocks of the Canberra region became dry land and were eroded.
You can see this former land surface as unconformity between the State Circle Shale and the Camp Hill Sandstone. The Camp Hill Sandstone was deposited on this former land surface after the sea flooded this area and a shallow sea was formed. At about 420 million years before present the area was uplifted and was again faulted and folded. Since then erosion has created the present land surface and the sea has never returned to that region.
Logging Requirements: To log this cache please measure the vertical displacement on the two sides of the fault at S 35 18.290 E 149 07.668 (the location is almost under the bridge so the coordinates might not be very good but if you are right under the edge of the bridge you are in the correct spot!) and mail this information to me using the my Profile Page at Geocaching.com (Please do NOT use the new gc.com messaging service!) . If you are unsure what a fault is have a look at wikipedia, if you are unsure what to measure maybe my drawing helps...
One additional advice you have to go to the location under the edge of the bridge, it will not be possible to get the measurement done from the other side of the road or from the spot where the sign is! Furthermore you should take a photograph of yourself with your GPSr and the State Circle Outcrop and post it together with your log. As this may no longer be mandatory (as per the change in the guidelines you can log without it, however if I have serious doubts that you were not there to solve the task and just guessed your answer I may delete your log if you did no post a photo...
You can provide the answer to the question in your email either in english or german and of course you can log here in any language you like... I hope you enjoy this Earthcache & Thanks to Greg the reviewer of this Cache for improving it!
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